How can you tell when you've got it right? How difficult is adjusting the hight? Is it as simple as getting under the car and just tweaking a switch?

Telling you have it right just entirely depends on what you like. What I think is perfect may be completely different for someone else. As for ride height change, for the front you have to raise the car up remove the wheels and use the supplied wrenches in the kit to adjust the height. The rear just needs to be raised up to adjust.